Heat exchanger



P 1962 P. SOUDAN ETAL 3,053,512

HEAT EXCHANGER Filed April 5, 1959 PA UL SOUDA N HE NR! MERGIER INV EN TORS AT ORNE Y United States Patent Ofifice 3,353,512 Patented Sept. 11, 1962 3,053,512 IEAT EXCHAN GER Paul Soudan, Aix-en-Provence, and Henri Mercier, Ga

danne, France, assignors to Pechiney, Cmpagnie de Produits Chimiques et Electrometallurgiques, Paris,

France, a corporation of France Filed Apr. 3, 1959, Ser. No. 803,887 Claims priority, application France Apr. 9, 1958 6 Claims. (Cl. 257-154) This invention relates to a heat exchanger and more particularly to a heat exchanger which is especially suitable for applications in industries in which liquids must be cooled or heated while being stirred.

Heat exchange is a problem which is common to almost all industries, but presents particular difliculties in chemical engineering applications where viscous liquids or suspensions of solids in liquids are used and in which these materials must be heated or cooled while being stirred. Difficulty is especially experienced when the materials which must be treated tend to encrust the apparatus. These and other ditficulties of the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a heat exchanger Which is particularly effective and efficient in operation.

Another object of this invention is the provision of a heat exchanger for use in heating or cooling viscous liquids or suspensions of solids in liquids while they are being stirred, the heat exchanger being capable of use even when the materials tend to encrust the apparatus.

A further object of the present invention is the provision of a heat exchanger which considerably increases the overall coefficient of heat transmission and yet which is easy to construct and maintain.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to certain of its structural forms as illustrated by the accompanying drawings in which:

FIG. 1 is a perspective view of the apparatus embodying the principles of the present invention;

FIG. 2 is a modification of the apparatus;

FIG. 3 is a further modification of the apparatus; and

FIG. 4 is a still further modification of the apparatus of the invention.

Referring first to FIG. 1, wherein are best shown the general features of the invention, the heat exchanger, indicated generally by the reference numeral is shown as consisting of an upper circular main header 17 and a lower main circular header 19 arranged in spaced, parallel relationship. An entrance tube 18 enters the upper main header 17 while an outlet tube leaves the lower main header. Arranged between the main headers are a series of sets 14- each of which consists of an upper circular secondary header 15 and a lower circular secondary header 16 joined by parallel tubes 13. A connecting tube 11 joins the lower secondary header 16 to the lower main header 19, while a connecting tube 12 joins the upper secondary header 15 to the upper main header 17, the connecting tube 12 being in the form of a spiral which is capable of considerable expansion and contraction lengthwise of the tubes 13-. It should be noted that the units 14 are arranged so that they are generally tangential to the outer surface of an imaginary cylinder joining the centerlines of the annuli which define the main headers 17 and 19.

The operation of the apparatus will now be readily understood in view of the above discussion. The heat exchanger unit 10 is intended to be placed in a chemical vessel (not shown) which also contains a stirring apparatus. It is supposed that the stirring apparatus will lie within the circle of the units 14 and the entire vessel will be filled with a chemical which may be a viscous liquid or a thick suspension of solids in a liquid. Depending upon the chemical process, it may be desirable either to heat or cool the liquid in the vessel for which purpose steam or hot water may be introduced into the heat exchanger or cooling liquid. In the case of cooling, the coolant enters the unit through the inlet tube 18 and fills the upper main header 17. It passes down through the individual connecting tubes 12 into the upper secondary headers 15 which distribute it to the individual tubes 13. The principal heat exchange actually takes place through the tubes 13 and the surrounding liquid in the vessel. The cooling liquid passes through the tubes from the upper end to the lower end and is collected in the lower secondary header 16 from which it passes through the connecting tube 11 into the lower main header 19. The coolant fluid then passes through the outlet tube 20' and is returned to its source. The procedure is similar if the fluid is a heating fluid. The stirring apparatus will cause a flow of the liquid in the vessel around the tubes 13 and produce heat exchange between the coolant fluid and the chemical fluid in the vessel.

FIGS. 2, 3, and 4 show variations of the shapes of the tubes in the units 14. For instance, in FIG. 2 a connecting tube 2.1 enters a secondary header 22 which is associated with tubes 23. As is evident in the drawings, the tubes 23 are formed with spiral corrugations which extend around the tubes. These spiral corrugations increase the heat exchange surface of the tubes and they, therefore, promote the flow of heat from a material exterior of the tubes to the fluid in the interior of the tubes.

In FIG. 3 a connecting tube 24- leads into an upper secondary header 25 which is connected to tubes 26. The tubes are connected to the header 25 in pairs, each pair lying in a plane Which is radial to the header 25; in other words, the centerlines of each pair of tubes lie in a plane which passes through the axis of an imaginary cylinder joining the centerlines of the upper and lower secondary headers. One of each pair is connected to the header 25 at the inner surface and the other of the pairs is connected to the header at the outer surface; the tubes, therefore, form concentric, generally cylindrical sets of tubes.

In FIG. 4 a connecting tube 27 is attached to a secondary header 28 to which are attached tubes 29. Each tube consists of a series of generally radial sections alternated with angular sections to form a zig-zag conformation.

It can be seen, then, that the heat exchanger of the present invention contains an improvement whose purpose is mainly in considerably increasing the overall coefficient of heat transfer. At the same time the construction and maintenance is rendered much easier. Another advantage of the new apparatus resides in an important reduction of the incrustation of heat exchange elements. Also, the heat exchanger, according to the invention, leads to a very large increase of exchange surface in comparison with conventional apparatus of a same capacity. It should be noted that the ratio of the diameter of each tube of the sets is much lower than the diameter of tubes used in presently known exchangers. When the ratio of diameter to the length of the tube is made low enough, the interplay of thermal expansion and contraction produces a vibration which is favorable for automatically removing incrustations from the heating surfaces. It can be understood that the units lie well J outwardly against the walls of the vessel where they are subjected to the greatest velocity of flow of the material being stirred in the vessel so that the heat exchange is greatest because of this greater velocity.

In one application of the invention, it was used for the alkaline digestion of bauxite under pressure wherein a suspension of powdered bauxite in alkaline liquor was heated within an autoclave provided with a stirrer. In substituting the present invention for the conventional series of peripheral tubes, an increase of 50% of the heating surface was obtained. Similarly, when conventional coils were replaced by the construction of the invention the total amount of heat transfer was increased by 100% (doubled). The autoclave had a diameter of 2.60 meters and was 8.5 meters in height. Fifteen sets were used each having twelve uniform tubes placed as shown in FIG. 1. Each tube was 55 millimeters in external diameter and was 6.4 meters long. This provided a heating surface within the autoclave of 200 square meters. A conventional heat exchanger would have only 130 square meters using 28 tubes of 200 millimeters diamter and 7.4 meters in height. The liquid in the autoclave had a density of 1.4 grams per centimeter and viscosity was 2 centipoises at 100 C. When the suspended liquor was heated from 200 C. to 230 C. with saturated steam at 235 C., an overall heat transfer coeflicient was obtained of 2,000 calories per square meter per hour per degree of centigrade, instead of 800 or 900 calories per square meter per hour per degree of Centigrade obtained with a conventional heat exchanger working in the same conditions.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

1. A heat exchanger, comprising an upper and a lower main circular header, the headers being arranged in spaced, parallel relationship, a series of sets joining the headers, each set comprising an upper and a lower circular secondary header considerably smaller in diameter than the said main headers, the headers in each set being arranged in spaced parallel relationship, and a series of thin, helically-shaped flexible tubes joining the secondary headers a thin, flexible tube joining each upper secondary header to the upper main header, a thin, flexible tube joining each lower secondary header to the lower main header, the flexible tubes being the sole support for each set.

2. A heat exchanger as recited in claim 1 wherein each set is related to the main headers so that most of its tubes lie outside of an imaginary cylinder joining the centerlines of the main headers.

3. A heat exchanger, comprising an upper and a lower main annular header, the headers being arranged in spaced, parallel relationship, a series of sets joining the headers, each set comprising an upper and a lower annular secondary header considerably smaller in major diameter than the said main headers, the headers in each set being arranged in spaced parallel relationship, a series of thin, flexible tubes joining the secondary headers, an expansible thin, flexible helicallyshaped inlet tube j0ining each upper secondary header to the upper main header, a thin, flexible outlet tube joining the lower secondary header to the lower main header, each set being related to the main headers that most of its tubes lie outside of an imaginary cylinder joining the centerlines of the main headers, the flexible inlet tube and the flexible outlet tube constituting the sole support for each set.

4. A heat exchanger as recited in claim 3 wherein each tube is formed with a spiral corrugation.

5. A heat exchanger as recited in claim 3 wherein the tubes are attached to the secondary headers in pairs, each pair being arranged in a radial plane, one being connected to the inner surface of the headers while the other is connected to the outer surface of the headers.

6. A heat exchanger as recited in claim 3 wherein each tube consists of radial portions alternated with angular portions to obtain a zig-zag conformation.

References Cited in the file of this patent UNITED STATES PATENTS 1,028,777 Power June 4, 1912 1,308,486 Earle July 1, 1919 1,884,777 Lucke Oct. 25, 1932 1,884,778 Lucke et al. Oct. 25, 1932 2,506,120 Turner May 2, 1950 2,621,900 Borg Dec. 16, 1952 2,640,686 Brown June 2, 1953 

